A body-implantable lead is used with an implantable cardiac device (ICD), such as an implantable pacemaker, a cardioverter, a defibrillator, a cardioverter defibrillator, and the like, to both sense cardiac function and deliver stimulation pulses to a desired tissue location. When the stimulating device is a cardiac pacemaker, for example, the lead, also referred to as a “pacing lead,” connects the pacemaker's electrical circuitry directly with a desired chamber of the heart. One or more electrodes at or near a distal end of the lead placed inside of the heart contact the cardiac tissue therein at the desired location. The electrode(s) are electrically connected via insulated conductors within the lead to an appropriate connector at a proximal end of the lead. After an implantable lead is transvenously or otherwise implanted at the proper tissue location, the connector at the proximal end of the lead is detachably inserted into an appropriate mating connector of a medical device, such as a pacemaker, thereby electrically coupling the desired tissue location to the electrical circuits within the medical device.
The distal tip of the implantable lead is held at a desired tissue location by either active fixation or passive fixation. Active fixation (sometimes called “positive fixation”) involves the use of some type of mechanism or means, such as a helix or hook, for actively securing and holding the body tissue in contact with the distal tip. The most common type of active fixation is achieved using a screw-in helix tip located at the distal end of the lead. Active fixation is achieved by literally screwing the helix tip into the tissue. In contrast, passive fixation involves use of some type of mechanism or means, such as a tine assembly near the distal electrode, to lodge or passively fix the lead inside the heart. Tissue ingrowth can occur into the lead tip in order to firmly hold it in its desired position.
A common technique used to implant an active fixation lead is to insert the lead transvenously into the desired tissue contact location, e.g., inside of the heart. However, such transvenous insertion requires that the active fixation tip be maintained in a retracted position until the distal tip of the lead is at the desired tissue contact location. Otherwise, during the process of inserting the lead, the active fixation tip, comprising, e.g., a sharp, protruding screw-in helix tip, could easily become entangled with and/or damage delicate body tissue at a location other than the desired tissue contact location. Thus, many active fixation leads have extendable/retractable helix tips which may be retracted within or extended from the lead body, thereby allowing the helix tip to be shielded during implantation and exposed during fixation. A simple construction of such a lead incorporates a connector pin attached to a conductor coil of the lead that is in turn attached to a fixation helix. In order to extend the helix and anchor it into the heart tissue, a clip-on tool or implant tool is used to rotate the connector pin. Rotation of the connector pin rotates the conductor coil, which in turn rotates the fixation helix, thereby causing it to extend or retract. Many existing implant tools require the surgeon to count the number of rotations to achieve proper rotation of the connector pin. Many active fixation leads require about ten rotations of the connector pin to extend or retract the helix. Proper rotation of the connector pin is required to ensure fixation of the lead to the heart tissue, since excessive rotations can damage the connection between the helix and the coil or result in perforation, while too few rotations can result in improper fixation.
What is needed, therefore, is an implant tool for a lead, and method of using the same, that facilitates proper rotation of the connector pin to ensure fixation of the active fixation tip to the body tissue.